Whole-Dwelling Ventilation Calculator (2019 Method)

Concepts behind this calculation

Calculate a dwelling ventilation rate with a named 2019 equation set, eligible Q50 infiltration credit and a continuous or repeating-hour fan schedule.

This dwelling calculation pins a particular 2019-method path rather than selecting an adopted requirement. Its total rate combines conditioned floor area with design occupancy based on bedrooms, with a minimum bedroom baseline and an increase for higher known occupancy. A lower known population does not reduce that baseline here.

An eligible, documented blower-door path can provide infiltration credit using the specified factors and attachment basis. Balanced and unbalanced arrangements use different credit treatment, including a scoped unbalanced exception. The hourly schedule converts the mechanical requirement to on-cycle capacity only for the same automatically repeated pattern every hour; an arbitrary daily runtime is a different exposure problem.

How to use this calculator

1. Document Edition and dwelling design basis; enter Conditioned dwelling floor area, Bedrooms, and Known design occupants (0 = use bedroom baseline).
2. Select Dwelling attachment, Ventilation arrangement, and Infiltration credit method.
3. For eligible credit, document Blower-door and factor source and enter Leakage at 50 Pa (Q50), Weather and shielding factor (wsf), Above-grade dwelling boundary height (H), and any applicable Horizontal-unit exterior boundary ratio (Aext).
4. Choose Fan operating schedule; for hourly operation, confirm Automatic hourly control confirmed? and enter On-time fraction of every hour before reviewing the required on-cycle airflow.

Calculation method and applicability

B = max(1, bedrooms); Ndesign = max(B + 1, known occupants). Qtot = 0.03Afloor + 7.5Ndesign. Qinf = 0.052Q50 × wsf × (H/8.2)^0.4. Qcalc = Qtot − Phi × Qinf × Aext, with Phi = 1 (balanced) or Qinf/Qtot (unbalanced). Qfan = max(0, Qcalc); for the cited unbalanced-credit branch Qcalc ≤ 15 CFM invokes its exception and Qfan = 0. For an identical repeating-hour cycle, Qon = Qfan/f and ton = 60f.

Input definitions and units

Edition and dwelling design basis

Identify the actual adopted edition/project basis and dwelling use. This calculator pins the 2019 equations with the cited erratum/Addendum h definitions. It does not select a current code edition.

Conditioned dwelling floor area (ft²)

Use dwelling floor area under the named method, not lot area or shared common areas.

Bedrooms (count)

Whole bedrooms; a studio is calculated using the one-bedroom minimum. The 100-bedroom bound is a tool limit, not a standard rule.

Known design occupants (0 = use bedroom baseline) (people)

The baseline assumes two people for a studio/one-bedroom unit, plus one per further bedroom. Higher known occupancy increases the rate at 7.5 CFM per extra person. Lower occupancy does not reduce it here.

Dwelling attachment

Only detached and qualifying horizontally attached dwellings can take this single-point credit. Stacked/other attachment can use the no-credit rate. Choices: Detached; Horizontally attached only; Stacked or other attachment.

Ventilation arrangement

Balanced means simultaneous supply and exhaust within 20% under the cited definition. Otherwise select unbalanced. This changes the infiltration superposition factor and the scoped 15 CFM exception. Choices: Balanced supply and exhaust; Unbalanced exhaust or supply.

Infiltration credit method

Choose no credit unless an eligible dwelling and qualifying single-point blower-door test are documented. Local exhaust deficits and other credits are outside this page. Choices: No infiltration credit; Qualifying single-point Q50 test.

Blower-door and factor source

Required when credit is selected: document ASTM E1827 or ANSI/RESNET/ICC 380 basis, test/date, actual Appendix B factor source and location, and boundary dimensions. Example factor 1 is illustrative, not a geographic default. Applies to Infiltration credit method: Qualifying single-point Q50 test.

Leakage at 50 Pa (Q50) (CFM)

Measured qualifying 50 Pa test flow. No guessed ACH50, dwelling volume default or exterior-only measurement is inferred. Applies to Infiltration credit method: Qualifying single-point Q50 test.

Weather and shielding factor (wsf) (factor)

Supply the factor from the selected edition's Normative Appendix B or a verified project source. The calculator contains no location/weather table. Example 1 is illustrative. Applies to Infiltration credit method: Qualifying single-point Q50 test.

Above-grade dwelling boundary height (H) (ft)

Vertical distance from the lowest to highest above-grade dwelling-boundary points. Reference height is 8.2 ft. Do not substitute ceiling height automatically for a multistory unit. Applies to Infiltration credit method: Qualifying single-point Q50 test.

Horizontal-unit exterior boundary ratio (Aext) (fraction)

For eligible horizontal attachment: boundary area not attached to garages or other units divided by total dwelling boundary area. Detached Aext is always 1 and ignores this field. Applies to Infiltration credit method: Qualifying single-point Q50 test; Dwelling attachment: Horizontally attached only.

Fan operating schedule

Continuous, or one identical automatically controlled on/off cycle repeated every hour. Extended and irregular schedules require a separate exposure method. Choices: Continuous; Identical repeating one-hour cycle.

Automatic hourly control confirmed?

Confirm only if the same on/off fraction repeats every hour. The tool will withhold the schedule result if unconfirmed; output does not verify a real controller. Choices: Not confirmed — withhold hourly sizing; Confirmed identical automatic hourly cycle. Applies to Fan operating schedule: Identical repeating one-hour cycle.

On-time fraction of every hour (fraction)

Between 0 and 1 inclusive of 1. For example 0.5 means 30 minutes on every hour. The on-cycle fan must deliver the displayed airflow; nominal fan CFM is not a measurement. Applies to Fan operating schedule: Identical repeating one-hour cycle.

How to interpret the result

Distinguish total rate, usable credit, pre-exception value, and mechanical rate. For a confirmed hourly cycle, on-cycle CFM is the capacity to deliver during operation, not the annual or daily average.

Worked examples

Assumptions and limits

• This page implements one named baseline/single-point calculation path, not every provision of Standard 62.2 or its latest edition. Alternative local-exhaust compliance, filtration credit, multipoint leakage, arbitrary extended schedules, common areas and current jurisdictional adoption remain outside the implemented path.
• The infiltration equation and 15 CFM unbalanced exception use the 2019 erratum and 2022 Addendum h text. Historical 2013 Addendum m and 2010 Addenda n/u are cited separately for baseline/occupancy/hourly-method provenance; they are not labeled current standalone standards.
• Credit eligibility is enforced for detached/horizontal-only attachment. Detached Aext=1. Horizontal-unit factors, actual test compliance and source-table weather factors still need documented project data; entering a reference does not authenticate them.
• The higher-occupancy adjustment is included conservatively. Lower known occupancy never reduces the baseline here; such a reduction requires a separately approved basis. Tool limits of 100 bedrooms and 1,000 occupants are numeric/usage bounds, not standard occupancy limits.
• Only the identical automatic one-hour pattern is sized. Its average across any three-hour window equals Qfan under the repeating pattern; this does not validate extended-cycle exposure, daily duty fractions, actual fan airflow or controller operation.
• The signed equation result, capped usable credit and scoped exception are shown separately. A zero mechanical result from the selected method is not permission to omit a system under other standards, local exhaust requirements or project obligations.

Sources

• PNNL / DOE Building America — 62.2-2019 Tool GuideDwelling task, single-point eligibility, hourly solver and excluded alternative/multifamily paths. This guide is context, not the equation text.
• ASHRAE 62.2-2019 Addendum h (2022)Equations 4-2/4-3, Q50 test standards, Aext/Phi, attachment eligibility and unbalanced 15 CFM exception.
• ASHRAE 62.2-2019 erratum (27 February 2020)Confirms that the selected Phi numerator is Qinf, not Qfan.
• ASHRAE 62.2-2013 Addendum m (historical baseline provenance)Explicit Qtot area/bedroom equation and no-negative-mechanical-rate guidance. Cross-checked against the 2019 CEC public equation text; not treated as current local law.
• ASHRAE 62.2-2010 Addendum n (historical occupancy provenance)Minimum one-bedroom handling and higher known occupancy adjustment. The lower-occupancy alternative is not implemented.
• ASHRAE 62.2-2010 Addendum u (historical short-term-cycle provenance)Time-average and automatic short-term-cycle basis; this tool supports only a repeating hourly subset. PNNL 2019 guide also describes hourly runtime solving.